1. Field of the Invention
The present invention relates to an image processing apparatus for processing a gradation image.
2. Related Background Art
A known approach for attaining the stability of an image is by forming a chrominance pattern on a photosensitive body, and reading the density of its pattern and feeding back image forming conditions such as .gamma.-compensation.
However, in the conventional example indicated above, since it was impossible to take into account the deviation relating to a machine body, such as variations in sensor sensitivity and fluctuations in the distance between a sensor and an object to be measured, the level at which the image is stabilized may differ from machine to machine.
In particular, in the cases of copiers of electrophotographic system, as well as printers (for example, ink jet printer) or other systems, various characteristics of a processing means such as photosensitive body and developer may vary with the number of times it is used.
Besides, in the conventional example described above, when a gradation reproduction method for a screen angle of pulse width modulation is changed depending on modes such as character-line block mode and photography mode, for example, required according to the kind of manuscript, the chrominance pattern on an image carrier differs in its reflection characteristic depending on various gradation reproduction methods, so that it was not possible to correctly detect density in different modes so long as the same density detecting method is used. As the result, it was impossible to constitute an accurate feedback system.
Needless to say, a reflection characteristic of the chrominance pattern on the image carrier, such as photosensitive body, also differs depending on image forming material such as toner or the like.